Analogs of the tetradecapeptide somatostatin will be synthesized and tested for their effects on the secretion of pituitary growth hormone, pancreatic insulin and glucagon, and hormones of the gastrointestinal system, notably gastrin and secretin. On the basis of these studies, conclusions will be drawn as to the relationship between the structure of the somatostatin molecule and its numerous biological activities. This should enable us to design analogs possessing more specific actions and, hence, far greater usefulness than the natural hormone. For instance, analogs exhibiting enhanced inhibition of GH might be useful in the treatment of acromegaly and angiopathies associated with diabetes mellitus, those primarily inhibiting glucagon secretion for treatment of diabetes mellitus, those inhibiting insulin for treatment of hyperinsulinism and those inhibiting gastrin and gastric acid secretion in the treatment of ulcers. Another primary objective would be the parallel development of somatostatin analogues of considerably greater biological half-life than the natural hormone. In addition, the possibility of preparing competitive inhibitors of somatostatin will be investigated.